The United States Court of Appeals for the Second Circuit has released a secret Obama administration memorandum detailing the legal justification for a 2011 drone strike in Yemen that killed Anwar al-Awlaki, an al-Qaida leader born in the U.S.

The memo concludes that al-Awlaki's citizenship would not preclude the U.S. from "taking lethal action" against him, based on facts about the case submitted by the CIA, Department of Defense, and intelligence community. This summation of legality is predicated on the U.S. government's declaration of al-Awlaki as an "operational leader" of an "enemy force" — al Qaeda.

The memo, prepared by the Justice Department's Office of Legal Counsel, says that because the U.S. government considered al Awlaki to be an "operational leader" of an "enemy force," it would be legal for the CIA to attack him with a drone "as part of the United States' ongoing non-international armed conflict with al Qaeda," even though he was a U.S. citizen.

The memo also says the killing of al Awlaki by U.S. military forces would be legal under an authorization for the use of U.S. military force approved by Congress following the Sept. 11, 2001, attacks on New York and Washington, D.C.

According to the memo, a U.S. citizen like al-Awlaki would be protected by the Fifth Amendment's due-process clause, as well as the Fourth Amendment, even while he is abroad. But the memo states a "decision-maker," such as President Barack Obama, could "reasonably conclude" that al-Awlaki's actions posed a "continued" and "imminent" threat to the United States.

"In addition to the nature of the threat posed by al-Aulaqi's activities, both agencies here have represented that they intend to capture rather than target al-Aulaqi if feasible; yet we also understand that an operation by either agency to capture al-Aulaqi in Yemen would be infeasible at this time," the memo reads.

The release of the memo comes after the White House allowed senators to see it amid a fight over the nomination of David Barron to fill a seat on the U.S. Court of Appeals for the First Circuit. Barron, who was then the acting chief of the Justice Department's Office of Legal Counsel, wrote multiple opinions in support of the use of drones against American citizens, including this one.

Citing from the Supreme Court case Hamdi v. Rumsfeld, Barron wrote that "the realities of combat" render certain uses of force "necessary and appropriate," including against U.S. citizens who have become part of enemy forces —and that "due process analysis need not blink at those realities.

The memo's release also comes in response to a suit from The New York Times and the American Civil Liberties Union. Jameel Jaffer, the ALCU's deputy legal director who argued the case, said the memo's release marked a "crucial step toward transparency."

"There are few questions more important than the question of when the government has the authority to kill its own citizens," Jaffer said. "This memo’s release will allow the public to better understand the scope and implications of the authority the government is claiming. We will continue to press for the release of other documents relating to the targeted killing program, including other legal memos and documents relating to civilian casualties."